[antlr-interest] Re: Local lookahead depth
Oliver Zeigermann
oliver at zeigermann.de
Sun Nov 9 23:22:53 PST 2003
--- In antlr-interest at yahoogroups.com, "lgcraymer" <lgc at m...> wrote:
> > >>2.) Sometimes using tree transformation is too expensive
> > >
> > >
> > > Sometimes it is overkill (unnecessary development), but too
> > > expensive? I doubt it, especially for languages where lexing
> and
> > > parsing are complex. [BTW, my experience is that
> unsubstantiated
> > > performance arguments are usually bogus and made in an attempt
> to
> > > subjectively win an argument that cannot be won on the basis of
> > > objective evidence.]
> >
> > I have the same experience. But consider extremely large amounts
> of
> > input to be parsed. In this case it is prohibitve to generate an
> AST
> > because of the memory issue. As a very practical exmaple I have
> parsing
> > of the AMM (Aircraft Maintenance Manual) which is available in
> SGML
> > (very hard to parse, really). I parsed this a few years using
> ANTLR, but
> > its size normally is around 100MB. A few years ago my machine had
> 128MB
> > of RAM! You see what I mean?
>
> And how much disk space did you have? On a UNIX box, mmap() is a
> good way of automating file I/O, but even on systems without virtual
> memory, you can fake it. Performance is not an issue--with a problem
> of this size, nothing stays in the processor cache, and the overhead
> of the disk writes will be only a few percent.
>
> --Loring
Loring,
are you really serious about this? Have a look at the DOM vs. SAX
discussion in the XML area...
Oliver
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